In industrial robots there are generally three distinguishable sets of cabling. Power cabling comprising a bundle of electric-power cables is arranged for driving the movements of the robot. This cabling may also comprise the supply of power for operating a tool carried by the robot. Signal cabling comprising a bundle of signal cables is arranged for controlling the robot and the tool. Finally, process cabling is also arranged, comprising electric cables, hoses, pressure tubes or the like for supply of energy, pressure medium, coolant, etc., for the tool. Normally, the first two types of cabling are laid, protected, inside the manipulator. The process cabling is, however, normally coarser and less bendable and must, in addition, be capable of being easily replaced, so this cabling is fixed outside the manipulator. However, this location entails a risk of the cabling being damaged. It is also exposed to wear.
In manipulators, there is a general problem of ensuring the supply of the tool during all the movements of the manipulator for a long period of time. The greatest single reason for disturbances of the production of robots are hose and cable breakdowns of the process cabling at the wrist. Traditional suspension devices for process cabling often encroach in an adverse manner upon the working range of the robot. When the robot is performing more extreme hand movements, the cabling is also subjected to great tensile stresses and is subjected to wear against the rotor arm.
A special problem exists in anthropomorphic robots, where the upper axis rotates around its own longitudinal axis. In such robots, the cabling must be capable of being wound up around the upper arm. In such contexts, it is usual for the arm to be able to rotate, from an initial position, more than half a turn in both directions. The line bundle must therefore extend along the envelope surface of the robot arm. When the arm is in its neutral position, the necessary length is equal to the length of the arm. During rotation half a turn, however, the required length increases. The increase corresponds to the case where the line bundle, during rotation, must be laid half a turn around the envelope surface of the robot arm. This distance constitutes half the circumference of a circle with a radius defined by the distance between the axis of rotation and the center of the line bundle. A calculation shows that the required length of the line bundle becomes between 20 and 50% longer than the arm itself.
A surplus of the cabling must thus be arranged such that it can be wound around the upper arm when this arm is rotated. Usually, this surplus of cabling is arranged in a loop. When thus the cabling, during rotation of the upper arm, is wound up thereon, the cabling is stretched to the maximum extent. When the upper arm is in its initial position, the cabling is slack and the surplus then forms a loop. It is not unusual for this loop to exceed half a meter. This loop of the cabling often encroaches upon the working range of the rotor. During operations of the robot, the loop is often set into oscillation. It may then get stuck in objects within the working range. A freely oscillating loop is also subjected to fatigue, which may lead to failure in the cables.
From U.S. Pat. No. 4,705,243 (KUKA), an industrial robot is previously known, in which a plurality of holders are arranged for holding and guiding a line bundle from the stand to the tool. The majority of holders are rotatably fixed directly to the robot structure. The line bundle is adapted to run in loops between the holders. These loops ensure that the line bundle may follow all the movements of the manipulator.
One of the holders is rotatably attached to a resilient arm, which in turn is rigidly attached to the upper arm of the robot. The task of this robot is to hold a loop of the line bundle at a distance from the robot and allow the loop to accompany it during rotation of the upper arm. Since the arm itself consists of a spiral spring, the arm allows a deflection when stretching the cabling. In case of a minor deflection, the holder follows a circular path with its center in the attachment of the arm at the robot. In case of a major deflection, the bending center is moved further out on the resilient arm. The angular change of the holder thus increases progressively with the deflection. Large buckling loads are thus imparted to the cabling when the resilient arm is deflected.
An additional manipulator is known from the patent document WO098/19090 (ABB, Springmann), in which the cabling is running in a tube. This tube has a spring arranged in it, which exerts a returning attractive force on the cabling such that its slack is held on one side of the tube and which is usually directed backwards from the hand of the robot. In this way, the cabling is allowed to run back and forth in the tube while the spring exerts a force which all the time tends to hold the cabling stretched from the tube and up to the hand. The known robot has a complicated design and involves a drawback when replacing the cabling. The cabling is also worn during the movement in the tube.